The present invention relates to a particle beam irradiating apparatus having a charge suppressing device for irradiating a particle beam to a specimen and more particularly to an apparatus for irradiating a particle beam which is especially suitable for neutralizing an insulated specimen or a workpiece which is not connected to earth potential in a vacuum.
When a particle beam irradiating device irradiates a particle beam such as an ion beam or an electron beam with a high velocity to a specimen which is made from an insulator or a workpiece which is not connected to the earth potential in order to analyze or process the specimen, generally almost all of the specimen is positively charged.
For example, in the case of a secondary ion mass spectrometer, ion microprobe analyzer, ion implanter etc., the specimen is irradiated with a positively charged ion beam, emits secondary electrons from the surface of the specimen, and is positively charged.
In the case of the electron microscope or the electron beam lithography system, the specimen is positively charged when more secondary electrons than irradiated electrons are emitted from the surface of the specimen.
The above-mentioned positive charge of the specimen causes some bad effects with the specimen such as a breaking down of the specimen or obstacles in the correct irradiation of the particle beam to the specimen.
Methods of preventing the positive charge of the specimen and neutralization thereof are generally known. U.S. Pat. Nos. 4,118,630, 4,135,097 and 4,463,255 are cited as examples of such systems.
However, in the conventional methods stated above, it is very difficult to determine the electrons current supplied from a charged suppressing device. The positively charged specimen is not neutralized when the electron from the suppressing device are few in number, and the specimen is apt to be negatively charged when the electrons are excessively supplied.
U.S. Pat. No. 4,675,530 shows how to control the electron current supplied from the charge suppressing device by detecting the charge build up on the surface of the specimen. But it is difficult to detect the charge on the surface accurately and to control the electrons from the charge suppressing device so as not to charge positively or negatively, while considering stray capacitance of the chamber which stores the specimen.